In the Powder Metallurgy industry (PM industry) powdered metals, most often iron-based, are used for production of components. The production process involves compaction of a powder metal blend in a die to form a green compact, ejecting the compact from the die and sintering the green compact at temperatures and under such conditions that a sintered compact having sufficient strength is produced. By using the PM production route costly machining and material losses can be avoided compared to conventional machining of components from solid metals as net shape or nearly net shape components can be produced. The PM production route is most suitable for the production of small and fairly intricate parts such as gears.
In order to facilitate the production of PM parts lubricants may be added to the iron-based powder before compaction. By using lubricants, the internal frictions between the individual metal particles during the compaction step are reduced. Another reason for adding lubricant is that the ejection force and the total energy needed in order to eject the green part from the die after compaction are reduced. Insufficient lubrication will result in wear and scoring at the die during the ejection of the green compact leading to destruction of the tool.
The problem with insufficient lubrication can be solved mainly in two ways, either by increasing the amount of lubricant or by selecting more efficient lubricants. By increasing the amount of lubricant, an undesired side effect is however encountered in that the gain in density through better lubrication is reversed by the increased amount of the lubricants. A better choice would then be to select more efficient lubricants.
U.S. Pat. No. 6,395,688 to Vidarsson describes a process for producing a composite lubricant including a meta stable phase of a first lubricant chosen from saturated and unsaturated fatty acid amides or bisamides and a second lubricant chosen from the group of fatty acid bisamides. By melting the components and subjecting the melt to rapid cooling a meta stable lubricating phase is obtained.
U.S. Pat. No. 6,413,919 to Vidarsson discloses a process for the preparation of lubricant combination including the steps of selecting a first lubricant and a second lubricant, mixing the lubricants and subjecting the mixture to such conditions that the surface of the first lubricant is coated with the second lubricant.
Japanese patent application 2003-338526, publication no 2005-105323, teaches a lubricant combination of a core material of a low melting point lubricant, the surface thereof covered with particles of a high melting point lubricant.
WO 2007078228 describes an iron-based powder composition containing a lubricant which contains a lubricating core having the surface thereof coated with fine particulate carbon material.